Vacuum interrupter modules are used to control the application of large amounts of electrical power to an electrical load. These vacuum interrupters are maintained within an electrically insulated housing so as to prevent them from encountering environmental elements, such as snow and rain, as well as from encountering other debris that may interfere with the operation of the vacuum interrupter. To achieve such operation, the housings are typically made from a non-metallic material, such as ceramic or epoxy, which has been found suitable for electrically insulating the interrupter module.
To facilitate the mounting of the interrupter module, the housings are typically mounted to a platform or other base where the vacuum interrupter module can be rigidly affixed. Different manners for enabling the attachment of the interrupter module have been utilized. One way of attachment is to provide a mounting flange at the base of the interrupter module housing which provides a plurality of mounting bores. Furthermore, in some circumstances, the housing may provide mounting flanges at each end of the housing to facilitate the series coupling of multiple interrupter modules. However, housing designs have long suffered from being too fragile, such that the mounting flange, as well as other parts of the housing, are highly susceptible to fracture upon tightening of the bolts received through the mounting bores. For example, as the mounting bolts are torqued down to fasten the housing to a suitable base, the mounting flange becomes stressed causing it to deflect. The deflection of the mounting flange results in a fracture developing in the flange, which is permitted to propagate along a radius located between a bore in the flange through which the fastener is received and the main body of the housing. Unfortunately, however the propagation of the fracture is permitted to continue until it reaches the edge of the flange, thus resulting in the structural failure of the mounting flange.
Over the years, manufacturers have transitioned from fabricating the housing from ceramic based materials to epoxy based materials. Unfortunately, this transition has proved to have had a minimal effect on making the housing and mounting flange more resistant to fractures. As such, current vacuum interrupter module housings are still highly susceptible to fracture when the associated fasteners are exposed to a relatively minimal amount of torque.
Thus, in an effort to prevent the fracturing of vacuum interrupter module housings in light of the known deficiency in its structure, manufacturers have adopted torque specifications for the mounting bolts. For example, many current interrupter module housing designs require that the torque applied to the bolts received within the mounting bores be limited to approximately 25 in-lbs so as to reduce the likelihood of fracturing the mounting flange. However, such torque specifications employed in the industry are comparatively low, and thus, such a restriction on fastening torque may inadvertently be exceeded during installation or operation resulting in a fractured flange of the module housing.
Furthermore, because of the comparatively low amount of torque permitted to be applied to the fastening bolts, the torque settings on the tools used to fasten the bolts must be calibrated with increased precision to ensure that the bolts are fastened to their upper torque limit to prevent loosening over time. Furthermore, because the bolts are fastened to their upper torque limit, should the attachment flange be subjected to external forces, such as wind or that from external debris, the attachment flange may fracture due to stress sustained thereby, which may lead to the failure of the vacuum interrupter module.
Additionally, past designs of the vacuum interrupter module housings have been configured with the electrical handling and isolation properties of the housing in mind. As such, designers of the housings made the paths for which leakage current can pass made as long as possible and of equal length. Such a design was implemented so as to minimize the amount of leakage current that is permitted to pass over the surface of the housing and to ensure that the current loss of the housing would be minimized.
While the design of existing interrupter module housings have been optimized to minimize leakage currents in a controlled manner, other aspects of the housing design, in particular the structural aspects, have not been give the same amount of consideration. And it is for this reason that there still exists a long-felt need for a vacuum interrupter housing that is structurally resistant to fractures in and about its mounting flange.
Therefore, there is a need for a housing for a vacuum interrupter that eliminates sharp transitions between the mounting flange and housing body so as to prevent the development and propagation of fractures in the interrupter module housing. Additionally, there is a need for a housing for a vacuum interrupter module that provides at least one mounting flange that provides mounting bores that can receive fasteners that can be tightened with increased torque without fracturing the mounting flange. In addition, there is a need for a housing for a vacuum interrupter module that provides a curved transition between a housing body and at least one mounting flange that extends therefrom. In addition, there is a need for a housing for a vacuum interrupter module that provides at least one mounting flange that includes at least one mounting aperture disposed within a contoured counterbore at least partially disposed within a curved transition between the body and the at least one mounting flange.